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seqlock: seqcount_t: Implement all read APIs as statement expressions

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The sequence counters read APIs are implemented as CPP macros, so they
can take either seqcount_t or any of the seqcount_LOCKNAME_t variants.
Such macros then get *directly* transformed to internal C functions that
only take plain seqcount_t.

Further commits need access to seqcount_LOCKNAME_t inside of the actual
read APIs code. Thus transform all of the seqcount read APIs to pure GCC
statement expressions instead.

This will not break type-safety: all of the transformed APIs resolve to
a _Generic() selection that does not have a "default" case.

This will also not affect the transformed APIs readability: previously
added kernel-doc above all of seqlock.h functions makes the expectations
quite clear for call-site developers.

Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200904153231.11994-4-a.darwish@linutronix.de
This commit is contained in:
Ahmed S. Darwish 2020-09-04 17:32:29 +02:00 committed by Peter Zijlstra
parent 5cdd25572a
commit 52ac39e5db
1 changed files with 45 additions and 49 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

94
include/linux/seqlock.h
View file

@ -184,6 +184,12 @@ __seqprop_##lockname##_ptr(seqcount_##lockname##_t *s) \
return &s->seqcount; \
} \
\
static __always_inline unsigned \
__seqprop_##lockname##_sequence(const seqcount_##lockname##_t *s) \
{ \
return READ_ONCE(s->seqcount.sequence); \
} \
\
static __always_inline bool \
__seqprop_##lockname##_preemptible(const seqcount_##lockname##_t *s) \
{ \
@ -205,6 +211,11 @@ static inline seqcount_t *__seqprop_ptr(seqcount_t *s)
return s;
}
static inline unsigned __seqprop_sequence(const seqcount_t *s)
{
return READ_ONCE(s->sequence);
}
static inline bool __seqprop_preemptible(const seqcount_t *s)
{
return false;
@ -250,6 +261,7 @@ SEQCOUNT_LOCKNAME(ww_mutex, struct ww_mutex, true, &s->lock->base)
__seqprop_case((s), ww_mutex, prop))
#define __seqcount_ptr(s) __seqprop(s, ptr)
#define __seqcount_sequence(s) __seqprop(s, sequence)
#define __seqcount_lock_preemptible(s) __seqprop(s, preemptible)
#define __seqcount_assert_lock_held(s) __seqprop(s, assert)
@ -268,21 +280,15 @@ SEQCOUNT_LOCKNAME(ww_mutex, struct ww_mutex, true, &s->lock->base)
* Return: count to be passed to read_seqcount_retry()
*/
#define __read_seqcount_begin(s) \
__read_seqcount_t_begin(__seqcount_ptr(s))
static inline unsigned __read_seqcount_t_begin(const seqcount_t *s)
{
unsigned ret;
repeat:
ret = READ_ONCE(s->sequence);
if (unlikely(ret & 1)) {
cpu_relax();
goto repeat;
}
kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX);
return ret;
}
({ \
unsigned seq; \
\
while ((seq = __seqcount_sequence(s)) & 1) \
cpu_relax(); \
\
kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX); \
seq; \
})
/**
* raw_read_seqcount_begin() - begin a seqcount_t read section w/o lockdep
@ -291,14 +297,12 @@ static inline unsigned __read_seqcount_t_begin(const seqcount_t *s)
* Return: count to be passed to read_seqcount_retry()
*/
#define raw_read_seqcount_begin(s) \
raw_read_seqcount_t_begin(__seqcount_ptr(s))
static inline unsigned raw_read_seqcount_t_begin(const seqcount_t *s)
{
unsigned ret = __read_seqcount_t_begin(s);
smp_rmb();
return ret;
}
({ \
unsigned seq = __read_seqcount_begin(s); \
\
smp_rmb(); \
seq; \
})
/**
* read_seqcount_begin() - begin a seqcount_t read critical section
@ -307,13 +311,10 @@ static inline unsigned raw_read_seqcount_t_begin(const seqcount_t *s)
* Return: count to be passed to read_seqcount_retry()
*/
#define read_seqcount_begin(s) \
read_seqcount_t_begin(__seqcount_ptr(s))
static inline unsigned read_seqcount_t_begin(const seqcount_t *s)
{
seqcount_lockdep_reader_access(s);
return raw_read_seqcount_t_begin(s);
}
({ \
seqcount_lockdep_reader_access(__seqcount_ptr(s)); \
raw_read_seqcount_begin(s); \
})
/**
* raw_read_seqcount() - read the raw seqcount_t counter value
@ -327,15 +328,13 @@ static inline unsigned read_seqcount_t_begin(const seqcount_t *s)
* Return: count to be passed to read_seqcount_retry()
*/
#define raw_read_seqcount(s) \
raw_read_seqcount_t(__seqcount_ptr(s))
static inline unsigned raw_read_seqcount_t(const seqcount_t *s)
{
unsigned ret = READ_ONCE(s->sequence);
smp_rmb();
kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX);
return ret;
}
({ \
unsigned seq = __seqcount_sequence(s); \
\
smp_rmb(); \
kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX); \
seq; \
})
/**
* raw_seqcount_begin() - begin a seqcount_t read critical section w/o
@ -355,16 +354,13 @@ static inline unsigned raw_read_seqcount_t(const seqcount_t *s)
* Return: count to be passed to read_seqcount_retry()
*/
#define raw_seqcount_begin(s) \
raw_seqcount_t_begin(__seqcount_ptr(s))
static inline unsigned raw_seqcount_t_begin(const seqcount_t *s)
{
/*
* If the counter is odd, let read_seqcount_retry() fail
* by decrementing the counter.
*/
return raw_read_seqcount_t(s) & ~1;
}
({ \
/* \
* If the counter is odd, let read_seqcount_retry() fail \
* by decrementing the counter. \
*/ \
raw_read_seqcount(s) & ~1; \
})
/**
* __read_seqcount_retry() - end a seqcount_t read section w/o barrier